Inter-observer variability in systematic nodal dissection: comparison of European and Japanese nodal designation

Systematic nodal dissection is accepted as an important component of the intrathoracic staging of patients undergoing thoracotomy for lung cancer. Several lymph node maps have been proposed in an attempt to ensure uniformity in designating lymph node stations. The Japan Lung Cancer Society has published detailed definitions for each nodal station adopting the Naruke map. However, since these definitions had not been interpreted into other languages, they have not been universally accepted. The objective of this study was to assess the inter-observer variability in the interpretation of lymph node stations.

A total of 424 lymph node stations were removed from 41 patients undergoing thoracotomy for non-small cell lung cancer. All nodal stations were labeled using the Naruke map. As each station was excised, it was designated in a blind fashion by one of two surgeons trained in the UK and one surgeon trained in Japan. The designation accorded to each nodal station was analyzed.

The total concordance was 68.5% (right side 67.0%, left side 69.9%). The concordance rate for individual nodal stations varied from 0% to 100%. Considerable discordance existed between the Japanese and European surgeons in the designation of nodal stations 2, 4, 8 and N1 station 12. In 14 (34.1%) patients, discordance in the labeling of lymph nodes led to disease being categorized as N1 by one observer, whereas the other considered the same nodes to be N2.

Considerable discordance in the designation of nodal station has been demonstrated. We would expect similar inter-observer variability elsewhere between surgeons, institutions, or countries. More detailed nodal charts and precise, easily understood definitions of nodal stations are needed for intrathoracic staging. The first English version of the Japan Lung Cancer Society staging manual goes some way to address this.